1. Field of the Invention
This invention relates generally to clamps for positioning and holding work pieces during manufacturing and, more particularly, to clamps capable of automatically adjusting for holding work pieces of varying thicknesses.
2. Related Art
Manufacturing operations typically require that a work piece be held in place during machining, assembly and similar operations. Work pieces are held by presses, dies and, most commonly, by clamps. Many of these manufacturing operations are still hand operated. Thus, repetitive clamping of multiple work pieces for repetitive machining or assembly procedures creates predictable needs for efficiency, speed and ease of use.
This creates a need for automatic adjustment of a holding device, such as a clamp, to accommodate work pieces of various thicknesses and to thereby avoid the otherwise required re-positioning by hand of a clamp or the like. Work pieces of varying thicknesses necessarily result simply due to manufacturing tolerances. There is a particular need for minimizing or eliminating repetitive adjustments of clamping members when alternating between work pieces intended to be of various thicknesses.
Prior art clamps which will securely clamp work pieces having a minimally varying thickness include U.S. Pat. No. 3,212,347 to Robeson. This patent discloses a clamp having a spring to mediate the pressure applied by a plunger to a work piece. However, the plunger in that clamp may not be mounted in other clamps. Moreover, the compression of the spring cannot be readily adjusted and instead is fixed at the time of manufacture.
Worker safety is and virtually always has been a serious concern. Work piece holding devices are generally safer to the extent that they can eliminate pinch points where a worker may pinch his hand, especially in those applications where re-positioning of the work pieces into and out of the device may be done repetitively and at speed. Prior art clamps, to the extent that they use springs to compress a plunger and bias it towards a work piece generally do not enclose the spring, and thereby expose workers to pinch points. Another aspect of worker safety involves equipment design that reduces the risk of repetitive motion injury by reducing the necessary amount of force a worker must exert to engage a clamp. The prior art devices not providing some adjustability in spring force, or otherwise not allowing for some mechanical advantage place the worker at risk for this kind of injury as well.
There is thus a need in the art for a clamp to apply various degrees of pressure to accommodate work pieces made of various materials in order to prevent damage to the work pieces from excessive pressure. There is also a need to avoid movement of the work piece from its desired position by the type of sudden application of force often produced by toggle clamps or locking clamps. A holding apparatus, such as a clamp, that gradually exerts pressure on a work piece with a “soft start,” is needed. There is also a need for a clamp that will have a totally encapsulated spring, thus avoiding pinch points, but which can provide a soft clamping and accommodate variously sized work pieces. Still further there is a need for a clamp that is easily assembled, and which can be adjusted to provide a different clamping pressure.